1. Field of the Invention
The present invention relates to an engine case including: a crank chamber of an engine; a clutch chamber having a wet clutch connected to an output shaft protruding from the crank chamber; and a partition wall keeping the crank and clutch chambers separated and connecting the crank and clutch chambers.
2. Description of the Related Art
For prior art techniques relating to this type of engine case, there can be mentioned Japanese Unexamined Patent Application Publication No. 11-115517 (see paragraphs [0042]-[0044] and FIG. 5). The engine case described in this patent document has a first partition wall at least partially separating a crank chamber from a wet clutch, and a second partition wall separating the wet clutch from a V-belt continuously variable transmission. Engine oil stored in the crank chamber is sent by an oil pump, and supplied to a clutch chamber through a radial oil passage formed inside the second partition wall and an axial oil passage formed in the crankshaft (output shaft), to thereby lubricate various portions of the wet clutch. Through a portion near a lower end of the first partition wall, a communicating passage penetrates that communicates the crank chamber with the clutch chamber, and superfluous engine oil discharged from the wet clutch is allowed to return to the crank chamber through the communicating passage. It should be noted that the above-described patent document does not specifically describe where the oil inlet for engine oil should be located, but from the viewpoint of the general technique, it is presumed that the oil inlet is located in a portion of an outer wall of the crank chamber.
However, in the engine case described in the above-described patent document, it is necessary to form oil passages inside the crankshaft that extend in axial and radial directions and to secure an oil passage between an output shaft of the wet clutch and an input shaft of the transmission mechanism. Accordingly, remarkably high processing accuracy has been required.
In addition, in the case of the engine case described in the above-described patent document, at an early stage of starting of the engine after feeding the engine oil from the oil inlet, the engine oil is distributed in the crank chamber while the engine oil is not yet distributed over various portions in the clutch chamber. Since the engine is operated under this condition, the clutch should be in an off-state to perform a pre-conditioning interim operation that does not burden the engine, until a sufficient amount of the engine oil is distributed over the various portions in the clutch chamber.